1. Field of the Invention
Anticoccidial drugs have been used for the prevention of coccidiosis in poultry for many years. Although these programs have generally been considered effective, the development of resistance by avian coccidia to the drugs in current use has resulted in continued losses by the poultry industry to the disease. There is thus a strong incentive to develop more effective anticoccidia products and processes that will provide better protection against challenge by virulent field strains. This invention relates to preparations of the plant Echinacea purpurea which serve as novel dietary supplements for enhancing the effectiveness of vaccines against coccidia species and to methods utilizing these preparations in vaccination protocols.
2. Description of the Related Art
Coccidiosis in poultry is a disease resulting from infection by avian coccidia. These microorganisms are parasitic protozoa, and those belonging to the genus Eimeria are economically the most important and include E. acervulina, E. mivati, E. mitis, E. praecox, E. hagani, E. necatrix, E. maxima, E. brunetti and E. tenella. Eimeria tenella is the most pathogenic of the group and has thus received the most attention.
Although coccidiosis occurs in both invertebrates and vertebrates, including man, the poultry industry has been particularly affected by the disease, with coccidiosis being the most economically important parasitic disease of chickens. Problems associated with the disease are varied and range from poor feed conversion and reduced weight gain and egg production in light infections to morbidity and mortality in heavier infections. The parasite has an asexual/sexual life cycle which occurs in the intestinal tract of an infected bird. Infection occurs when birds ingest sporulated oocysts which are generally associated with fecal material. During the digestive process, the oocysts rupture, releasing asexual sporozoites into the digestive tract. Sporozoites subsequently invade epithelial cells of the intestinal tract where they eventually mature and release merozoites back into the digestive tract. Merozoites differentiate into gametocytes, thus initiating the sexual stage of the coccidia life cycle. The gametocytes fuse to produce the fertilization product, oocysts, which are released into the feces, or droppings, of infected birds. The formation of oocysts completes the life cycle of the parasite. Sporulation within the oocyst may then occur followed by transmission of the disease through ingestion by a new host. Characteristic digestive tract lesions are produced by the developing asexual and sexual stages.
Prevention or treatment of the disease by administration of anticoccidial agents such as ionophore drugs has generally been successful in the past, however, the development of drug-resistant strains has presented new challenges. A number of vaccines have been developed, including both live (virulent and attenuated), antigenic components and various recombinants. Schaap et al. (U.S. Pat. No. 6,203,801, Mar. 20, 2001) disclosed a 25-kd Eimeria polypeptide which may be used as an immunogen. Danforth, H. D. (1998. J. Parasitol. vol. 28, pp. 1099-1109) disclosed live oocyst vaccines using a virulent field strain isolate of E. maxima, while Danforth et al. (1997. Parasitol. Res. vol. 83, pp. 445-451) described evaluations of a four-species (E. acervulina, E. maxima, E. necatrix and E. tenella) virulent oocyst vaccine. Anderson et al. (U.S. Pat. No. 5,709,862, Jan. 20, 1998) disclosed recombinant antigenic peptides containing a determinant or determinants for use as vaccines.
Echinacea purpurea has been known for more than a century as a medicinal herb, and extracts from the plant have been implicated in immune-type responses. Purified polysaccharide fractions from Echinacea were reported to activate macrophages (Stimpel et al. 1984. Infect. Immun. vol. 46, pp. 845-849), to mediate action of the phagocyte system (Roesler et al. 1991. Int. J. Immunopharmac. vol. 13, pp. 27-37 and 931-941) and to protect against systemic infections in immunosuppressed mice (Steinmxc3xcller et al. 1993. Int. J. Immunopharmac. vol. 15, pp. 605-614). These studies were all carried out in mammalian (either human or mouse) systems, however, and there are no reports of effects on avian systems.
Although vaccine development represents significant progress in controlling coccidiosis, the disease continues to present problems for the poultry industry and results in considerable economic loss. There is thus a need to provide products and processes which are capable of improving resistance to the disease.
We have discovered that ingestion of preparations of Echinacea along with immunization provides significant advantage over immunization alone. In accordance with this discovery, it is an object of the invention to provide a method of treating birds to provide resistance to coccidiosis by the administration of both Echinacea and a vaccine to the birds.
It is also an object of the invention to provide a composition comprising Echinacea in amounts effective for providing resistance to coccidiosis when ingested in combination with immunization.
Other objects and advantages of the invention will become readily apparent from the following description.